Method and system for adjusting electrical components using alternately applied signals

ABSTRACT

A crystal filter or similar electrical component is adjusted by application to the filter of a characteristic adjusting medium, such as evaporated or sputtered gold, in order to provide a desired differential insertion loss with respect to output signals corresponding to two input signals generated at two frequencies of interest. The two input signals are applied sequentially to the filter with the signal levels of the input signals calibrated to differ by a quantity equal to the desired differential insertion loss. An initial calibration, utilizing a signal attenuator, provides this differential. Treatment then occurs, with the output of the crystal being continuously monitored by a signal amplitude measuring device. An AC monitoring signal, representing the alternating output signal levels corresponding to the sequentially applied input signals, is generated from the signal amplitude measuring device. A phase reversal in the AC monitoring signal is sensed by a phase detector, which generates a control signal to terminate the treatment operation. The phase reversal occurs at the instant that the desired differential insertion loss value is attained.

United States Patent [72] Inventor Robert P. Grenier Newburyport, Mass.

[21] Appl. No. 889,211

[22] Filed Dec. 30, 1969 [45] Patented Aug. 17, 1971 [73] AssigneeWestern Electric Company, Incorporated New York, N.Y.

[54] METHOD AND SYSTEM FOR ADJUSTING ELECTRICAL COMPONENTS USINGALTERNATELY APPLIED SIGNALS Primary ExaminerEdward E. KubasiewiczAttorneys-W. M. Kain and R. P. Miller ABSTRACT: A crystal filter orsimilar electrical component is adjusted by application to the filter ofa characteristic adjusting medium, such as evaporated or sputtered gold,in order to provide a desired differential insertion loss with respectto output signals corresponding to two input signals generated at twofrequencies of interest. The two input signals are applied sequentiallyto the filter with the signal levels of the input signals calibrated todiffer by a quantity equal to the desired differential insertion loss.An initial calibration, utilizing a 9Clai 10Drawin Fi 8 gs signalattenuator, provides this differential. Treatment then [52] 0.8. CI324/57 R, occurs, ith th t t f th t l b i ti l 29/2535, 118/9 324/56monitored by asignal amplitude measuring device. An AC [51] Int. Cl...G01n 27/00 monitoring signal, representing the alternating outputSignal {50] Field of Search i. 324/56, 57; levels corresponding t thsequentially applied input signals, 29/2535 574i is enerated from the sinal amplitude measurin device. A

h l'hA C "'l' db p ase reversa in t e monitoring signa IS sense y a [56]References cued phase detector, which generates a control signal toterminate UNITED STATES PATENTS the treatment operation. The phasereversal occurs at the in- 2,l78,225 10/1939 Diehlet al. 324/56 stantthat the desired differential insertion loss value is at- 2,794,9526/1957 Golden et al. 324/57 tained.

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Ilg-s I l I I I I I I l l FREQUENCY MOP q FREQUENCY FREQUE NC I METHODAND SYSTEM FOR ADJUSTING ELECTRICAL COMPONENTS USING ALTERNATELY APPLIEDSIGNALS BACKGROUND OF THE INVENTION This invention relates to methodsand systems for adjusting electrical components and, more particularly,to methods and apparatus for testing one or more electrical components,such as piezoelectric crystal filters, while adjusting each component soas to provide desired frequency response characteristics to thecomponent.

In the production of piezoelectric crystal filters and similar articles,it may be desired that a given differential insertion loss be providedwith respect to output signals corresponding to two input signals at twodifferent frequencies of interest. Ordinarily, a crystal filter unitprovides initially a differential insertion loss value departingconsiderably from that desired. Treatment operations must, therefore, beperformed with respect to each filter in order to alter the frequencyresponse characteristics of the filter so as to attain the desireddifferential insertion loss.

The treatment of a crystal filter to vary the differential insertionloss will normally affect simultaneously the frequency responsecharacteristics of the filter at both frequencies of in terest.-Monitoring both of these quantities simultaneously, comparinginstantaneous values of the quantities and terminating treatment atexactly the correct instant to provide the desired result constitutes acomplex operation which would be most difficult for an individual tocontrol. Automatic systems and methods for performing these tasks would,clearly, be most advantageous.

SUMMARY OF THE INVENTION An object of the invention resides in new andimproved methods and systems for testing one or more electricalcomponents, e.g., piezoelectric crystal filters, while adjusting eachcomponent so as to provide desired frequency response characteristics tothe component.

The invention contemplates adjustment of crystal filters or similararticles by treating each such component with a characteristic adjustingmedium, for example, evaporated or sputtered gold for varyingthe massand other physical properties of the component. During the treatmentoperations, the response of the crystal filter or other component to thetwo frequencies of interest is continuously monitored by an alternatingapplication of signals at the two frequencies to the filter. The methodsand systems contemplated by the invention function to terminateautomatically the treatment operation when a desired differentialinsertion loss is attained for the crystal filter.

The invention further contemplates an initial calibration operationwherein the input signals are caused to differ in signal level by aquantity equal to the desired differential insertion loss. The treatmentoperation, with the alternating application of the signals to thetreated crystal filter, follows. An AC monitoring signal, representingthe amplitudes of the alternating outputs corresponding to thealternated input signals, is generated. A phase reversal in the ACmonitoring signal, indicating that the desired differential insertionloss has been attained, causes a control signal to be generated,terminating the treatment operation. The differential insertion loss is,thus, fixed for the treated crystal at the desired value. The phasereversal provides a simple and reliable indication that the requiredfinal condition of the filter has been achieved.

BRIEF DESCRIPTION OF THE DRAWING FIGS. 1 and 2 are block diagrams ofalternative embodiments of a system constructed in accordance with theprinciples of the invention for carrying out a method of the inventionfor adjusting frequency response characteristics of electricalcomponents, such as crystal filters;

FIGS. 3 through 5 are insertion loss versus frequency curvesillustrating a typical crystal filter during various phases of operationof the systems of FIGS. 1 and 2; and

FIGS. 6 through 10 are waveforms depicting the operations of variousportions of the'system of FIGS. 1 and 2 under varying circumstancesrelating to the operation of these systems.

DETAILED DESCRIPTION Referring to FIG. 1 of the drawing, there isillustrated an arrangement for testing'and adjusting the response of acrystal filter or other electrical component to input signals at twofrequencies of interest, f and f so as to provide to the crystal filtera desired differential insertion loss between the resulting outputsignals. Two conventional signal sources 11 and 12 provide the signalsat the respective frequencies f and f and at adjustable output levels.Typically, the two signal frequencies may be 8, 155, 200 Hz. and 8, 154,200 Hz., while the desired differential insertion loss may be 3 db. The3 db. differential insertion loss value will be used as an example inthe following discussion.

A filter holder 13 is provided for the crystal filter, which filter maybe composed of a material such as quartz. The crystal filter is to betreated by appropriate treatment apparatus 14 for adjusting the responseof the filter toward the desired differential insertion losscharacteristic. Such treatment apparatus 14 may, by way of example,apply an adjusting medium, e.g., evaporated or sputtered gold, to thecrystal filter under the control of any suitable process controlcircuitry 16. The method and apparatus of the invention will operate todetect the response of the crystal filter to the input signals providedby the signal sources 11 and 12 and to generate a control signal,causing the process control circuitry 16 to effect a termination of theadjustment operation by the treatment apparatus 14, when the crystalfilter has acquired the desired differential insertion losscharacteristic.

The illustrative apparatus of FIG. 1 includes a switch 17 operablebetween two conditions under the control of a conventional square wavegenerator 18. In a first condition of the switch 17, the signal source11 will be coupled to the filter holder 13, either directly through aline 19 or through a 3 db. attenuator pad 21, depending upon thecondition of a pair of associated switches 22 and 23. In a secondcondition of the switch 17, the signal source 12 will be coupled to thefilter holder 13. The square wave generator will function to alternatethe switch 17 between these two conditions. It should be noted that theattenuator pad will attenuate the signal from the source 11, whencoupled to thissource, by a value equal to that desired for thedifferential insertion loss, i.e., 3 db.

Also included in the apparatus of FIG. 1 is a conventional signalamplitude detector 24, which is coupled to receive output signals fromthe crystal filter in the holder 13 through an amplifier 26. Two lowfrequency AC amplifiers 27 and 28 are coupled to receive output signalsfrom the amplitude detector 24. The amplifier 27 is, in turn, coupled toan AC voltmeter 29, while the amplifier 28 is coupled to aconventional-phase detector 31. The arrangement is such that the phasedetector 31 will be utilized to provide the control signal to theprocess control circuitry 16 for terminating the adjustment operation bythe treatment apparatus 14.

Turning now to FIGS. 35 of the drawing, it is desired that an exemplarydifferential insertion loss of 3 db. be provided by a treated crystalfilter when input signals at frequencies f and f, are applied to thefilter. This condition is illustrated in the insertion loss versusfrequency curve of FIG. 5.

A typical initial characteristic curve of a quartz crystal filter unitis shown in FIG. 3. The differential insertion loss is, clearly, muchgreater than the desired 3 db. value with respect to 1 and f inputsignals. By appropriate treatment of the filter, a relatively highinsertion loss portion of the characteristic curve may be shifteddownwardly in frequency from the position shown in FIG. 3, through anumber of intermediate stages such as that illustrated in FIG. 4, so asto provide the desired insertion loss versus frequency relationshipdepicted in FIG. 5.

This shift may be provided by deposition of gold or another materialonto the quartz crystal, the mass of the deposited material affectingthe frequency response characteristics of the filter.

A typical method of operating the exemplary apparatus of FIG. 1, inaccordance with the principles of the invention, involves an initialcalibration procedure. The signal source 11 is coupled initiallydirectly to the switch 17 through the line 19, the associated switches22 and 23 being positioned in the depicted condition of FIG. 1. Thesquare wave generator 18 is now operated, causing the switch 17 tocouple alternatingly or sequentially to the holder 13 the first inputsignal from the signal source 11 at frequency f and the second inputsignal from the signal source 12 at frequency F The holder 13 ispresently short circuited, e.g., through a crystal filter bypass line 32associated with the holder, such that the two signals are coupledsequentially to the amplitude detector 24 and the AC voltmeter 29, whilebypassing a crystal filter retaining portion of the holder 13. Thesystem is calibrated by increasing or decreasing the output level of oneof the sources 11 and 12 until equal output signal amplitudescorresponding to the two sequentially applied input signals are observedat the amplitude detector 24, as represented by a zero voltage readingon the AC voltmeter 29.

The calibrated system may now be utilized to adjust a crystal filter,initially having the loss versus frequency curve of FIG. 3, to providethe desired insertion loss versus frequency curve of FIG. 5. The crystalfilter to be adjusted is introduced into the filter holder 13, while thebypass line 32 is disconnected, e.g., by operating a switch 33. Thus,the filter will be coupled through the amplifier 26 to the insertionloss monitoring and treatment control portions of the system.

The associated switches 22 and 23 are, meanwhile, operated to anopposite condition from that illustrated in FIG. 1. In this manner, thesignal source 11 of the frequency f signal is coupled to the switch 17through the switch 22, the 3 db. signal attenuator 21 and the switch 23.Operation of the switch 17 under the control of the square wavegenerator will now couple the unattenuated f frequency signal and the ffrequency signal, attenuated by 3 db. alternatingly to the holder 13 forthe crystal filter to be adjusted.

The apparatus is presently in a condition of operation suitable forcrystal filter treatment, i.e., with the signal attenuator 21 coupledbetween the signal source 11 and the switch 17, with a crystal filter tobe adjusted positioned in the filter holder 13 and with the switch 33operated to couple signals from the switch 17 to the held crystal. Thetreatment apparatus 14 is now rendered effective to commence treatingthe crystal filter, e.g., by vacuum deposition or sputtering of goldonto the filter, to vary the characteristic curve of FIGS. 3 through ina manner toward attaining the desired FIG. 5 condition.

Referring next to FIGS. 6 through 10, several sample waveforms aredepicted. FIG. 6 represents the effect of the square wave generator 18and the signal attenuator 21 upon the output from the switch 17. The twoinput signals, at frequencies f, and f are alternatingly applied to thecrystal filter in the holder 13 at a 3 db. signal level differential.

FIG. 7 illustrates the output from the crystal filter applied to theamplitude detector 24 at the start of the adjustment opera tion providedby the treatment apparatus 14. The insertion loss property of the filterat the frequency f as may also be observed from FIG. 3, initiallyexceeds that at frequency f, by an amount greater than 3 db. The FIG. 7waveform takes into account the 3 db. attenuation in the signal level ofthe frequency f, input signal, still indicating the presence of a signallevel output greater at frequency f than at frequency f FIG. 8represents the situation which would occur if treatment were notterminated upon attainment of the desired 3 db. differential insertionloss, i.e., at the FIG. 5 stage. Thus, the output of the treated crystalfilter would become greater at frequency f than at frequency f due tothe effect of the 3 db. attenuation of the frequency f, signal, sincethe true differential insertion loss of the treated crystal filter wouldbe less than 3 db. This may be seen by observing the trend of the curvesof FIGS. 3 through 5.

FIGS. 9 and 10 depict the amplitude detector output waveformscorresponding to the crystal filter output waveforms of FIGS. 7 and 8,respectively. These waveforms represent instantaneous differentialsignal level curves for alternating output signals corresponding toalternated input signals at the two frequencies f, and f A phasereversal may be noted between the FIG. 9 and FIG. 10 conditions. Thisphase reversal takes place, obviously, at the instant when the 3 db.calibrated input signal level difference is matched by the differentialinsertion loss for the frequency f, and f input signals applied to thecrystal filter in the holder 13. It is, thus, at the moment of phasereversal that the treatment operation must be terminated.

The amplitude detector 24 continuously provides an AC monitoring signal,corresponding initially to the waveform of FIG. 9 through the lowfrequency AC amplifier 28 to the phase detector 31. Upon the phasedetector sensing a phase reversal in the AC monitoring signal, the phasedetector provides a control signal to the process control circuitry 16,ter minating the adjustment process provided by the treatment apparatus14. The differential insertion loss of the crystal is, thus, fixed atthe desire 3 db. level of FIG. 5.

Turning now to FIG. 2 of the drawing, there is illustrated a modifiedarrangement of apparatus provided in accordance with the principles ofthe invention. The system of FIG. 2 is essentially similar to that ofFIG. 1 in most respects. Thus, elements 11, 12,13, 14, 16, 17, 18, 24,26, 27, 28, 29, 31, 32 and 33 are virtually identical, and aredesignated by like reference numerals, in both FIG. 1 and FIG. 2.

The embodiment of FIG. 2 departs from that of FIG. 1 in that the line19, the attenuator pad 21 and the associated switches 22 and 23 of theFIG. 1 arrangement are not utilized. These are replaced, in the systemof FIG. 2, by two calibrated adjustable attenuators 21A and 218 coupledbetween the signal source 11 or 12, respectively, and the switch 17.

The operation of the FIG. 2 embodiment is substantially similar to thatof FIG. 1. Either or both of the calibrated adjustable attenuators 21Aand 218 may be adjusted during an initial calibration operation toprovide a desired initial differential signal output level, e.g., 3 db.The treatment operation may then take places as previously described forthe FIG. 1 embodiment.

It is to be understood that the described apparatus and method aresimply illustrative of two alternative embodiments of the invention.Many modifications may be made in accordance with the disclosedprinciple of the invention. Thus, the technique involved may be adaptedto control any frequency-responsive characteristic of an electricalcomponent. Additionally, a modification of the described method might beprovided by calibrating a system similar to that of FIG. 1 while a db.signal attenuator device is coupled in series with one of the inputsignals. Cessation of such attenuation would provide the desired 3 db.signal level difference during a subsequent treatment operation.

What I claim is:

1. In a method of adjusting an electrical component so as to provide apredetermined differential insertion loss with respect to output signalscorresponding to two input signals generated at two differentfrequencies of interest, the steps of:

applying the two input signals sequentially to the electrical componentwith the signal levels of the two signals calibrated to differ by aquantity equal to the predetermined differential insertion loss; whiletreating the component so as to vary the response of the electricalcomponent to at least one of the frequencies; and while detecting thedifferential signal level between output signals of the electricalcomponent corresponding to the two frequencies;

generating a control signal upon the detected differential signal levelattaining a value of zero; and terminating the treating step upongeneration of the control signal.

2. In a method as set forthin claim 1, said detecting and control signalgenerating steps comprising: 7

, generating an AC monitoring signal corresponding to the sequentialsignal levels transmitted, by the electrical component as the two inputsignals are applied sequentially to the electrical component;

detecting a phase reversal in the AC monitoring signals; and

generating the control signal in response to the phase rever saldetection.

3. .In a method of utilizing a signal amplitude measuring device inadjusting an electrical component to provide a predetermineddifferential insertion loss between output signals corresponding to twoinput signals generated initially at like amplitude but at two differentfrequencies of interest, the steps of:

a. coupling one of the input signals in series through the electricalcomponent to the amplitude measuring device; then 7 b. measuring theamplitude of said one signal; next c. decoupling said one-input signalfrom the measuring device; thereupon d. coupling the other of the inputsignals in series through the electrical component to the amplitudemeasuring device through a signal attenuator selected'to attenuate said"other input signal by an amount equal to the predetermined differentialinsertion-loss; then emeasuring the amplitude of said other signal; andthen f. decoupling said other signal from the amplitude measuringdevices; thereupon g. repeatingly performing steps (a) through (f) anumber of times; while v altering a characteristic of the electricalcomponent affecting the differential insertion loss until equal outputsignal amplitudes are measured by the amplitude measurin device.

4. In a method as set forth in claim 3, said altering step comprising:

treating the electrical component in a mannerselected to vary saidcharacteristic of the electrical component; while generating an ACmonitoring signal corresponding to the alternating amplitudes measuredby the amplitude measuring device as the two input signals are appliedalternatingly to the electrical component;

generating a control signal in response to a phase reversal of the ACmonitoring signal; and

terminating the treatment of the electrical component in response togeneration of the control signal.

5. In a method of utilizing a signal amplitude measuring device inadjusting an electrical component so as to provide a predetermineddifferential insertion loss between output signals corresponding to twoinput signals generated at two different frequencies of interest, thesteps of:

coupling the two input signals sequentially to the amplitude measuringdevice;

' adjusting the relative amplitudes of the input signals to provideequal output signal amplitudes as measured by the amplitude measuringdevice; thereupon coupling the two input signals sequentially to theelectrical component with one of the input signals so coupled through asignal attenuator selected to attenuate said one input signal by anamount equal to the predetermined differential insertion loss; and

coupling the electrical component to the amplitude measuring device; andthereupon altering a characteristic of the electrical componentaffecting the differential insertion loss until equal output signalamplitudes are measured by the amplitude measuring device. 6. In amethod as set forth in claim 5, said altering step comnsrn p treatingthe electrical component in a manner selected to vary saidcharacteristic of the electrical component; while generating an ACmonitoring signal corresponding to the alternating amplitudes measuredby the amplitude measuring device as the two input signals are appliedalternatingly to the electrical component; and terminating the treatingof the electrical component upon the occurrence of a phase reversal inthe AC monitoring signal.

7. In a method as set forth in claim 6, said treating and terminatingsteps comprising:

applying a characteristic adjusting medium to the electrical component;

generating a control signal in response to a phase reversal in the ACmonitoring signal; and

discontinuing application of the characteristic adjusting medium to theelectrical component in response to generation of the control signal.

8. In a system for adjusting an electrical component so as to provide apredetermined differential insertion loss between output signalscorresponding to two input signals having two frequencies of interest:

means for generating signals having both of said frequencies of interestand including calibrating adjustment means for varying the output levelof at least one of the two signals;

means for attenuating a selected on of said signals by a quantity equalto the predetermined differential insertion loss;

means for detecting theamplitude of an output signal from v theelectrical component;

coupling means for selectively coupling the two signals in analternating manner to said amplitude detecting means externally of theelectrical component during a calibrating phase of operation of thecoupling means and for selectively coupling the two signals in analternating manner through the electrical component to the amplitudedetecting means during a treatment phase of operation of the couplingmeans, said coupling means, including switching means selectivelyoperable between two conditions of operation for coupling the amplitudedetecting means to receive said selected on signal bypassing the signalattenuating means in the calibrating phase of operation of the couplingmeans and for coupling the electrical component and the amplitudedetecting means to receive said selected one signal through theattenuating means in the treatment phase of operation of the switchingmeans;

means, initiated into operation during said treatment phase of thecoupling means, for treating the electrical component so as to alter acharacteristic affecting the differential insertion loss; and

means responsive to an equalization of the alternating amplitudesdetected by the amplitude detecting means upon application to theelectrical component of the two input signals alternatingly during saidtreatment phase of the coupling means for terminating the operation ofthe treating means.

9. In a system as set forth in claim 8, said terminating meanscomprising:

means responsive to the alternating amplitudes detected by the amplitudedetecting means as the two signals are applied alternatingly to theelectrical component for generating an AC monitoring signalcorresponding to said detected alternating amplitudes; and

means responsive to a phase reversal in said AC signal for discontinuingthe operation of the treating means.

1. In a method of adjusting an electrical component so as to provide apredetermined differential insertion loss with respect to output signalscorresponding to two input signals generated at two differentfrequencies of interest, the steps of: applying the two input signalssequentially to the electrical component with the signal levels of thetwo signals calibrated to differ by a quantity equal to thepredetermined differential insertion loss; while treating the componentso as to vary the response of the electrical component to at least oneof the frequencies; and while detecting the differential signal levelbetween output signals of the electrical component corresponding to thetwo frequencies; generating a control signal upon the detecteddifferential signal level attaining a value of zero; and terminating thetreating step upon generation of the control signal.
 2. In a method asset forth in claim 1, said detecting and control signal generating stepscomprising: generating an AC monitoring signal corresponding to thesequential signal levels transmitted by the electrical component as thetwo input signals are applied sequentially to the electrical component;detecting a phase reversal in the AC monitoring signals; and generatingthe control signal in response to the phase reversal detection.
 3. In amethod of utilizing a signal amplitude measuring device in adjusting anelectrical component to provide a predetermined differential insertionloss between output signals corresponding to two input signals generatedinitially at like amplitude but at two different frequencies ofinterest, the steps of: a. coupling one of the input signals in seriesthrough the electrical component to the amplitude measuring device; thenb. measuring the amplitude of said one signal; next c. decoupling saidone input signal from the measuring device; thereupon d. coupling theother of the input signals in series through the electrical component tothe amplitude measuring device through a signal attenuator selected toattenuate sAid other input signal by an amount equal to thepredetermined differential insertion loss; then e. measuring theamplitude of said other signal; and then f. decoupling said other signalfrom the amplitude measuring devices; thereupon g. repeatinglyperforming steps (a) through (f) a number of times; while altering acharacteristic of the electrical component affecting the differentialinsertion loss until equal output signal amplitudes are measured by theamplitude measuring device.
 4. In a method as set forth in claim 3, saidaltering step comprising: treating the electrical component in a mannerselected to vary said characteristic of the electrical component; whilegenerating an AC monitoring signal corresponding to the alternatingamplitudes measured by the amplitude measuring device as the two inputsignals are applied alternatingly to the electrical component;generating a control signal in response to a phase reversal of the ACmonitoring signal; and terminating the treatment of the electricalcomponent in response to generation of the control signal.
 5. In amethod of utilizing a signal amplitude measuring device in adjusting anelectrical component so as to provide a predetermined differentialinsertion loss between output signals corresponding to two input signalsgenerated at two different frequencies of interest, the steps of:coupling the two input signals sequentially to the amplitude measuringdevice; adjusting the relative amplitudes of the input signals toprovide equal output signal amplitudes as measured by the amplitudemeasuring device; thereupon coupling the two input signals sequentiallyto the electrical component with one of the input signals so coupledthrough a signal attenuator selected to attenuate said one input signalby an amount equal to the predetermined differential insertion loss; andcoupling the electrical component to the amplitude measuring device; andthereupon altering a characteristic of the electrical componentaffecting the differential insertion loss until equal output signalamplitudes are measured by the amplitude measuring device.
 6. In amethod as set forth in claim 5, said altering step comprising: treatingthe electrical component in a manner selected to vary saidcharacteristic of the electrical component; while generating an ACmonitoring signal corresponding to the alternating amplitudes measuredby the amplitude measuring device as the two input signals are appliedalternatingly to the electrical component; and terminating the treatingof the electrical component upon the occurrence of a phase reversal inthe AC monitoring signal.
 7. In a method as set forth in claim 6, saidtreating and terminating steps comprising: applying a characteristicadjusting medium to the electrical component; generating a controlsignal in response to a phase reversal in the AC monitoring signal; anddiscontinuing application of the characteristic adjusting medium to theelectrical component in response to generation of the control signal. 8.In a system for adjusting an electrical component so as to provide apredetermined differential insertion loss between output signalscorresponding to two input signals having two frequencies of interest:means for generating signals having both of said frequencies of interestand including calibrating adjustment means for varying the output levelof at least one of the two signals; means for attenuating a selected onof said signals by a quantity equal to the predetermined differentialinsertion loss; means for detecting the amplitude of an output signalfrom the electrical component; coupling means for selectively couplingthe two signals in an alternating manner to said amplitude detectingmeans externally of the electrical component during a calibrating phaseof operation of the coupling means and for selectively coupling the twosignals in an alternaTing manner through the electrical component to theamplitude detecting means during a treatment phase of operation of thecoupling means, said coupling means, including switching meansselectively operable between two conditions of operation for couplingthe amplitude detecting means to receive said selected on signalbypassing the signal attenuating means in the calibrating phase ofoperation of the coupling means and for coupling the electricalcomponent and the amplitude detecting means to receive said selected onesignal through the attenuating means in the treatment phase of operationof the switching means; means, initiated into operation during saidtreatment phase of the coupling means, for treating the electricalcomponent so as to alter a characteristic affecting the differentialinsertion loss; and means responsive to an equalization of thealternating amplitudes detected by the amplitude detecting means uponapplication to the electrical component of the two input signalsalternatingly during said treatment phase of the coupling means forterminating the operation of the treating means.
 9. In a system as setforth in claim 8, said terminating means comprising: means responsive tothe alternating amplitudes detected by the amplitude detecting means asthe two signals are applied alternatingly to the electrical componentfor generating an AC monitoring signal corresponding to said detectedalternating amplitudes; and means responsive to a phase reversal in saidAC signal for discontinuing the operation of the treating means.